Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$120.51	6.818%	$128.7264	$128.73	$128.75	$128.70
Purchase #2	$172.58	8.618%	$187.4529	$187.45	$187.45	$187.50
Purchase #3	$138.34	13.174%	$156.5649	$156.56	$156.55	$156.60
Purchase #4	$150.71	3.642%	$156.1989	$156.20	$156.20	$156.20
Purchase #5	$23.45	12.474%	$26.3752	$26.38	$26.40	$26.40
Purchase #6	$196.64	13.799%	$223.7744	$223.77	$223.75	$223.80
Purchase #7	$165.26	10.500%	$182.6123	$182.61	$182.60	$182.60
7 purchase totals =	$967.49		$1,061.7050	$1,061.70	$1,061.70	$1,061.80